Astronomy and Astrophysics for the 1970s Volume 1: Report of the Astronomy Survey Committee (1972) / Chapter Skim
Currently Skimming:
3. ASTROPHYSICAL FRONTIERS
3. ASTROPHYSICAL FRONTIERS
Pages 12-52
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 12... ...
But in the twentieth century when astronomers began to apply the laws of physics to the stars, they realized that the prodigious energy stars emit cannot be sustained indefinitely. Even with the most efficient nuclear power.
|
From page 13... ...
The great optical telescopes of the Western United States have shown that space is filled as far as they can see with galaxies rather like our own. Too faint to be seen with the naked eye, the most distant ones at 5 billion light years take many hours to register on film even with telescopes 10 mil· lion times as sensitive as the eye.
|
From page 14... ...
14 A STR ONOM Y A N D A ST R O PHY SI CS FO R Til E 197 o ·s .· .
|
From page 15... ...
Unfortunately, these eJfeets are discernable only for red shifts of the order of unity and, hence, for speeds approaching that of light, and there just are not enough galaxies of large red shift observed to discriminate between rival cosmologies. Construction of one or more additional large optical telescopes and instrumenting all large telescopes with fast electronic systems will permit progress on this problem.
|
From page 16... ...
Sci· enlists of Ihe Bell Telephone Laboratories. in attempting to eliminate all sources of noise fro m a sensitive radio telescope.
|
From page 17... ...
Astrophysical Frontier3 17 bulb. So far this has been verified with roughly 20 percent accuracy in the region from 21 em to 2.6 mm, although some discrepancies may have been observed in the far infrared.
|
From page 18... ...
As the gas cooled, clumps were then drawn together to form galaxies; among them our own Milky Way was born. Some of these galaxies exploded, and by looking back in time with large radio telescopes we can now detect these events as quasars and radio galuies.
|
From page 19... ...
Astrophysical Frontiers 19 recently formed galaxies, or even groups of galaxies, do exist. Perhaps some type of "new physics" may ye.
|
From page 20... ...
20 ASTRONOMY AND ASTROPHYS ICS FOR THE 1970's The solar corona photographed in visible light and x rays- a montage showlng the relationship between ground- and space-based observations. (Photo coul'lfiY ofAmeriam Scl~nu and Engineering, Inc., and High Altilude ObserWitory,)
|
From page 21... ...
A:stroplrysical Fronti~r$ 21 determination of helium abundance comes from a c~mieal analysis of the composition of the solas wind and cosmic rays by means of satellites. Abundance determinations from lhe solas specuum.
|
From page 22... ...
Interaction of fast particles with the plasma and with the imbedded magnetic fields produces a wide variety of phenomena that tire interesting ftom the s tand point of plasma physics and, mon."<::ver, offer us the opportunity to interpret comparable events in more distant and less·well·resolvcd objects. This interaction bet-ween plasmas and magnetic fields Is well observable in the very-short· and very·long·wavelength regions of the solar spectrum.
|
From page 23... ...
Astrophysical Fronti~l'$ 23 high temperatures. As was the case with the spectroscopy of the neutral or moderately ioniud atoms a few decades ago.
|
From page 24... ...
24 ASTRONOMY AND ASTROPHYS ICS FOR THE 1970's servation of the shape of the sun has led to the suggestion that the core of the sun still rotates at its primeval rapid rate. invisible beneath the slowly rotating surface.
|
From page 25... ...
possibly a relativistic "black hole." The sun and its planetary system condensed from the interstellar me· dium nearly 5 billion years ago. We are learning more about the "solar nebula," from which we came.
|
From page 27... ...
Astroplrysical Frontiers 27 to learn the original proportion of helium produced by the big bang. Hydrogen, stiU overwhelmingly the most abundant element in the universe.
|
From page 28... ...
Or. consider red giant stars located relatively near the center of our galaxy.
|
From page 29... ...
Astrophysical Frontiers 29 pyramid is built. It will require the closest attention to nearly every other branch of astronomy.
|
From page 30... ...
30 ASTRONOMY AND ASTROPHYSICS FOR TilE 1970'• A supernova remnant - the Crab pubat photographed by the 12Q.in. telescope.
|
From page 31... ...
Astrophysical Fro111ien 31 form a black hole; again, we have no firm evidence for this process, except for a suggestion of a black hole as a component of an x·ray source.
|
From page 32... ...
whose optical radiation was not understood until it was shown to be almost completely polarized and until the radio astronomers found it to be the third strongest radio sou= in the sky. The amorphous mass consists of tangled magnetic fields in which high-energy electrons spiral.
|
From page 33... ...
They supply the only known mechanism for efficient conversion of enormous amounts of gravitational potential energy into ,-ery-high-energy cosmic rays. The remnant pulsar at the center of the Crab nebula is still emitting over ten thousand times the solar luminosity into that nebula 900 years after the supernova explosion in which it was formed.
|
From page 34... ...
34 ASTRONOMY AND ASTROPHYSICS FOR THE 1970'• close to absolute zero: it has essentially no viscosity. negligible heat capacity.
|
From page 35... ...
he would be traveling so fast that he would have only a thousandth or a second for a glimpse of it whh the naked eye as he sped by. EXPLODING CORES OF GALAXIES Large optical and radio telescopes have discovered extraordinary phenomena in the centers of galaxies, the nearly pointlike nuclei.
|
From page 37... ...
as the universe expands from the cataclysmic event of whose wrenching paroxysm we are but dimly aware in the most remote and oldest reaches of space. To the astronomers of the 1930's and 1940's, these galaxies, grand and stately.
|
From page 38... ...
The system becomes denser, the near collisions and ejections more rapid , until the remaining stars undergo relativistic collapse into a black hole, releasing enormous amounts of gravitational energy. This dramatic picture is less radical in its physics than the speculation that a very large concentration of matter, such as is found at the center of a galaxy, may be the source of rapid, continuing creation of new matter.
|
From page 39... ...
to produce the radio noise is in the billion-volt range. and perhaps higher for x rays.
|
From page 40... ...
40 ASTRONOMY AND ASTROPHYSICS FOR TilE 1970's lntcnl |
From page 41... ...
Are there other molecules in space? Some, such as CH and CN, have strong absorption lines at optical wavelengths and were discovered early with the large spectrographs on conventional telescopes.
|
From page 42... ...
In addition, most complex molecules are easily broken apart by ultraviolet light and cosmic rays- it is only because our atmosphere shields us from this radiation that life can exist on earth. Yet with the decade of the 1970's barely begun, an undreamed-of array of complex forms has been found in interstellar space-molecules like formaldehyde, methyl alcohol.
|
From page 43... ...
High· sensitivity infrared and millimeter studies of such objects should pro•·e fruitful and may reveal the prime molecule factory. Other circumstellar dust clouds appear to be the remnants of protostars that have just formed.
|
From page 44... ...
The CJ |
From page 45... ...
Tests of general relativity may be carried out by radar ranging of planets passing close to and behind the solar limb. The signal returned has predictable delays caused by gravitational dencction, which differ in Einstein and Brans-Dicke cosmologies, and accurate observations will permit a definitive choice between the two theories.
|
From page 47... ...
The composition nnd isotope ratios in these planets could pro,•ide information a bout conditions in the primitive solar nebula. Scientists comntonly assume thnl.
|
From page 48... ...
A tie between friable meteorites and comets has been established through the study of meteor orbits; but it remains to be proven whether the type I carbonaceous chondrites are fragn1ents of extinct comet nuclei. One can see large questions about prelife organic chemistry and conditions in the solar nebula looming behind these studies.
|
From page 49... ...
Do civilizations indeed convert the material of their planetary system into the greatest possible living space and thus produce an unusual. perhaps easily detectable type of object in the sky?
|
From page 50... ...
ThiJ leads to the deduction lhat electromagnetic radiation is by far the most favorable communications mode. This argument can be carried further by observing that the quantum nature oflig.ht causes lo'•,.er electromagnetic frequencies to be more economical in transmitting information.
|
From page 51... ...
For example, the largest radio telescope, 1000 ft in diameter, could detect a civilization beaming signals with a similar tele· scope at a distance of some 1000 light-years. Some of the na1ural pulsar signals recorded by radio telescopes closely resemble signals that might be received from lransmitters of other civilizarions.
|
From page 52... ...
52 ASTRONOMY AND ASTROPHYSICS FOR T HE 1970'' ronstructlon of major facili ties,, such as a glant radio receiving array. a nd the operation of a project that will have as its goal the detection of in· lclligcnt life elsewhere.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.